System and method for fire detection

ABSTRACT

A system and method for detecting radiation indicative of fire, such as forest fire. In one embodiment, a threshold energy level is determined based on ambient sensor conditions. A sensor unit may be setup to scan a predetermined area for electromagnetic radiation. Any detected electromagnetic radiation may then be band pass filtered to a wavelength range centered about a predetermined frequency associated with the presence of fire. The resulting energy level signal may then be further filter to pass only those signals which exhibit a “flicker” frequency. If the resulting filtered signal exceeds the threshold signal, a fire notification signal may then be generated.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.10/492,155, filed Apr. 09, 2004, which based upon PCT InternationalApplication No. PCT/US02/32242, filed Oct. 10, 2002, which claims thebenefit of U.S. Provisional Application Ser. No. 60/328,436, filed Oct.10, 2001.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates generally to the detection of radiation energy,and more particularly to the use of radiation sensitive sensors todetect physical phenomenon such as emergent forest fires.

2. Description of Related Art

With cities around the world becoming more severely congested andpolluted, compounded by the high cost of living in urban areas,increasing numbers of the population are moving into the Wildland UrbanInterface (WUI)—those areas where forest and grasslands borderresidential development. The appeal of a rural setting and the privacyof a larger parcel of land provide an idyllic environment for manyfamilies.

However, as more families move into the WUI, there are an increasednumber of shared boundaries between population and wildland areas. Thishas resulted in an increased risk of wildfire that endangers structuresand lives. This is due in part to more human activity near wildlandareas which increases the chance of fire from human; carelessness orunavoidable accidents; fires started by natural causes, such aslightning; and aesthetic landscape preferences often place decorative,fuel rich trees and bushes in close proximity to structures.

Wildland firefighters were originally trained in conventional methodsand practices of dealing with wildfires in which there were minimalstructures and human habitation. However, much of the development in theWUI has been oriented toward the aesthetics of living in a forestedarea, and has not incorporated fire safety features in the design of theroads, water systems, structures or landscaping. For example, in orderto preserve the natural environment, road systems leading to the homesare often narrow and present difficult access challenges for multiplelarge, public safety vehicles in the event of an emergency. In view ofthese circumstances, there is increased reliance on homeowners to takemore responsibility for their personal safety and for the protection oftheir homes.

The changing role and level of risk of the firefighter in the growingWUI necessitates a rethinking of responsibilities for safety. Thecurrent trend is for the homeowner to take more responsibility for theirsafety by incorporating a defensible space around their dwellings. Thisincludes using landscaping that reduces fire risk by virtue of itslocation as well its level of fire resistance.

Increasing homeowner responsibility also necessitates incorporatingmeans for detecting and suppressing fires quickly when they occur. Thereare a number of gels and foam products that retard fires and can preventthem from burning down structures when applied properly. There are manysubstantiated instances in which a properly foamed or gelled homeescaped being burned by a voracious wildfire as it moved through theWUI. However, successful protection of a structure in a wildfire,regardless of the suppression technique employed, requires properadvanced notice and preparation. In the case of unoccupied homes, suchvacation homes, there are presently no effective means for providing thenecessary advanced notification of a proximate wildfire. Thus, there isa need for a system and method of providing the detection of a wildfireswhich avoids the aforementioned problems.

SUMMARY OF THE INVENTION

Disclosed and claimed herein are systems and methods for fire detection.In one embodiment, a method includes receiving electromagnetic radiationfrom an energy source, filtering the electromagnetic radiation to awavelength range centered about a predetermined frequency associatedwith the presence of fire, and generating an energy level signal basedon the received electromagnetic radiation. The method further includesfiltering the energy level signal to a flicker frequency rangeindicative of fire and comparing a magnitude of the energy level signalto a threshold value. In one embodiment, if the energy level signal isgreater than the threshold value, a fire notification signal isgenerated.

Other aspects, features, and techniques of the invention will beapparent to one skilled in the relevant art in view of the followingdetailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a function diagram of one embodiment of a sensor unit whichimplements one or more aspects of the invention;

FIG. 2 depicts one embodiment of the exterior of a unit constructed inaccordance with FIG. 1;

FIG. 3 is a block diagram functionally describing one embodiment of thesensor unit of FIG. 1;

FIG. 4 schematically illustrates one embodiment of directionalcalibration of the sensor unit of FIG. 1;

FIG. 5 is a sketch of a top view of FIG. 1 illustrating one embodimentof rotation in the horizontal plane;

FIGS. 6A-6B illustrate a flow diagram of an exemplary process forinitializing a detection system, consistent with the principles of theinvention;

FIG. 7 is one embodiment of flow diagram for carrying out radiationdetection operations, consistent with the principles of the invention;and

FIG. 8 is another embodiment of flow diagram for carrying out radiationdetection operations, consistent with the principles of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

One aspect of the present invention is to provide a system and methodfor detecting radiation indicative of fire, such as forest fire. In oneembodiment, a threshold energy level is determined based on ambientsensor conditions. In one embodiment, the threshold level may bedynamically adjusted, or alternatively may be static.

In one embodiment, a sensor unit is setup to scan a predetermined areafor electromagnetic radiation. Any detected electromagnetic radiationmay then be band pass filtered to a wavelength range centered about apredetermined frequency associated with the presence of fire, which inone embodiment is 4.3 microns in the infrared spectrum. The resultingenergy level signal may then be further filter to pass only thosesignals which exhibit a “flicker” frequency. In one embodiment, thisflicker frequency is indicative of fire and ranges between 1 and 10Hertz.

In another embodiment, or in addition to any of the previousembodiments, the magnitude of any detected energy level signal may becompared to the predetermined threshold value. If the energy levelsignal exceeds the threshold value, a notification signal indicating thepresence of fire may be generated. In one embodiment, the notificationsignal may also include location information since the infrared sensormay report its bearing at the time the threshold value was exceeded.

Another aspect of the invention is to provide a reliable technique forthe detection of fire which minimizes the occurrence of false positivereadings. In one embodiment, this may be done by causing the infraredsensor to sweep in a circular 360 degrees path, while pausing on each ofa series of bearings to take energy measurements. While each bearing canbe any size, in one embodiment each bearing spans approximately 6degrees. While paused at each bearing, a number of energy samples may betaken by the sensor. Using these energy samples, an energy value foreach bearings can then be computed, which in one embodiment is doneusing root mean square analysis. These energy values can then becompared to the threshold value. If the energy value for a given bearingexceeds the threshold value a predetermined number of times, the sensorunit may then enter a detect mode in which the bearing in question canbe further analyzed.

In one embodiment, while in the detect mode, the sensor unit takesadditional energy samples for the bearing in question over a longerperiod of time. After these additional energy samples have beennormalized, they may be compared against threshold value. If thethreshold value is again exceeded, a fire notification signal may begenerated.

As mentioned above, the detection of a large CO₂ signal at 4.3micrometers is suggestive of a fire. However, in order to distinguishspurious signals from 4.3 micrometer radiation of the type which may bedue to sun reflection or radiation emissions from heated CO₂ not arisingfrom an incipient forest fire, in one embodiment it may be helpful todetect whether the 4.3 micrometer signal has a “flicker” frequencyindicative of fire. In one embodiment, this “flicker” frequency isbetween 1 and 10 hertz. Additionally, a signal strength analysis (e.g.,a Root Mean Square analysis) of the output of the detector 12 may beused to provide for an initial determination of whether a fire has beendetected.

Still further discrimination may be necessary to determine whether thefire is a forest fire, a campfire or a hiker mischievously holding a litcigarette lighter in front of the radiation sensor. In one embodiment,this additional discrimination is based on a digital frequency analysisof the output of the IR detector. Both of these methods ofdiscrimination may be taken into consideration during the scanning bythe stepper motor 22 under the control of the microprocessor 35, as willbe further described below.

Via the scanning mechanism, the sensor signals from detector 12 for eachbearing may be smoothed by averaging, creating a background baselinereference. In one embodiment, each bearing is comprised of a six-degreeincrement. As shown in FIG. 5, each step of the mirror covers an angle αin the horizontal direction. With each subsequent step, an additionalbearing (e.g., six degrees) is covered, until a full 360° circle isaccomplished. During each step the output of detector 12 may beamplified and analyzed by microprocessor 35 after being processed by theRMS circuit 37. In another embodiment, before the scanning process canbegin, the sensor unit 1 is initialized. One embodiment of thisinitialization process will now be described with reference to FIG. 6.

1. System Overview

The sensor system 1 of FIG. 1 illustrate one embodiment of amicroprocessor-based sensor system which may be used to implement one ormore aspects of the invention. The sensor system 1 of FIG. 1 is depictedas having a single infrared radiation (IR) detector 12 receivingradiation from source 50 passing through sapphire window 17 andreflected by rotatable mirror 19. In one embodiment, the mirror 19provides 360° rotation in increments of 6 degrees, for example, bycontrol of the stepping motor 22. The vertical angle 2θ may have amagnitude determined by the sapphire window 17 and the vertical distancecovered by the length of mirror 19. In one embodiment, 2θ coversapproximately 90 degrees which, when sensor system 1 is positioned inthe forest environment, may be ±45 degrees from the horizontal.

For determining fire, radiation may be detected in a narrow frequencyband with a band pass centered at approximately 4.3 micrometers in theinfrared spectrum (IR). In one embodiment, the sensor system 1 providesthis narrow band sensitivity by using a detector 12 having a siliconwindow covered with two separate optical coatings. Each coating may havea separate but overlapping pass band. Additionally, there may be aseparate sapphire window which itself has a radiation pass band. As willbe described in more detail below, the basis for detection of a fire isthe emission of the CO₂ at 4.3 micrometers while normal atmospheric CO₂is absorptive at this particular wavelength. That is, solar radiation at4.3 micrometers is almost completely absorbed by the Earth's atmosphere.Therefore, detection of a large signal at 4.3 micrometers is suggestiveof a fire.

FIG. 2 depicts one embodiment of the exterior of a unit constructed inaccordance with FIG. 1. Conversely, FIG. 3 illustrates one embodiment ofthe various internal structural components of a system within the sensorsystem 1 of FIG. 1. In addition to the scanning mechanism 22, theinfrared detector 12, the analog amplifier 41, the root mean square(RMS) conditioning circuit 37 and the digital frequency convertingcircuit 32, a solar energy management system 57 functions, for example,in accordance with the energy management system of the above-describedU.S. Pat. No. 5,229,649. Output signals from the sensor system 1 aresent out through the radio/satellite modem output subsystem 55 to thefire control base station 75 terrestrially through a radio repeater 77or by way of a satellite to a satellite gateway 87.

The location of the sensor system 1 is determined based upon the GPSlocation information programmed into the system. In another variation,the sensor system 1 can include an external call button 47 which can bedepressed by a human to cause a radio signal to be sent. The systemwould then serve as a “call box” for injured or last hikers, woodsmen,and or others such as fireman in trouble who may have occasion torequire aid or make other approved or prearranged signals to a centrallocation. Additionally, the fire system sensor can be set up so that itis normally put into an alarm mode based on vandalism or tilt event. Thetilt and shock sensors 45 provide the mechanisms for such an alarmsystem.

In addition to providing notification of forest fires, the system isequally adaptable at providing indications of fires within confined orspecific areas by an alarm actuation as well as actuation of asuppression system such as water sprinkler system, a gel system or afoam system. Because of the above described scanning functionaccomplished by the signal fixed element which continues to scan afteran initial detection of fire, the system is able to not only indicatethe beginning of a fire, but also when a fire ceases to exist. This canbe particularly useful with respect to a water sprinkler system which,in the prior art, continues to operate until a shut-off is manuallyperformed, sometimes many hours after the fire has occurred. In mostenvironments, when a fire occurs and a sprinkler system is set off, themajor damage is due to water caused by the continuous sprinkleroperation. Using this detector, with its ability to continue scanningafter the beginning of a fire, allows for not only the output of thesignal to initiate the water sprinkler system, a foam system or a gelsystem but also to shut off the suppression system when the fire isextinguished.

This system allows for the control of a two-way valve to facilitatecontrol of a sprinkler/foam/gel system. The control of the two way valveis affected through an electromechanically actuated latching solenoidthat is controlled by signals from sensor system 1. The system may bewired directly to the sprinkler actuator or it may be set up for remoteoperation. It is also an advantage of this system that the sensorcontinues to scan even after a fire is extinguished so that, a sprinklersystem, foam system or gel system can be reactivated if the firereoccurs. Additionally, the ability to shut off the foam/gel systemallows for saving foam/gel because such systems have a limited storagecapacity.

Orientation calibration of the sensor can be accomplished, for example,using the opto device 96 shown in FIG. 4 in association with the mirror19. The opto device 96 include an optical sensor which directs lighttoward the spot 94 and receives the reflected light. This spot 94 may bemade of gold or some other material providing precise reflection to theopto device. The opto device 96 is used to calibrate the mirrorsrotational position and provides such information to the microprocessor35. Alignment to magnet north can now occur by rotating the mirror anadditional number of steps until the mirror is pointing at magneticNorth. This additional number of steps past the calibration point isstored by the microprocessor such that true fire bearing can be sent inan alarm situation. Other forms of self calibration with respect toNorth may be substituted.

2. Radiation Detection

As mentioned above, the detection of a large CO₂ signal at 4.3micrometers is suggestive of a fire. However, in order to distinguishspurious signals from 4.3 micrometer radiation of the type which may bedue to sun reflection or radiation emissions from heated CO₂ not arisingfrom an incipient forest fire, in one embodiment it may be helpful todetect whether the 4.3 micrometer signal has a “flicker” frequencyindicative of fire. In one embodiment, this “flicker” frequency isbetween 1 and 10 hertz. Additionally, a signal strength analysis (e.g.,a Root Mean Square analysis) of the output of the detector 12 may beused to provide for an initial determination of whether a fire has beendetected.

Still further discrimination may be necessary to determine whether thefire is a forest fire, a campfire or a hiker mischievously holding a litcigarette lighter in front of the radiation sensor. In one embodiment,this additional discrimination is based on a digital frequency analysisof the output of the IR detector. Both of these methods ofdiscrimination may be taken into consideration during the scanning bythe stepper motor 22 under the control of the microprocessor 35, as willbe further described below.

Via the scanning mechanism, the sensor signals from detector 12 for eachbearing may be smoothed by averaging, creating a background baselinereference. In one embodiment, each bearing is comprised of a six-degreeincrement. As shown in FIG. 5, each step of the mirror covers an angle αin the horizontal direction. With each subsequent step, an additionalbearing (e.g., six degrees) is covered, until a full 360° circle isaccomplished. During each step the output of detector 12 may beamplified and analyzed by microprocessor 35 after being processed by theRMS circuit 37. In another embodiment, before the scanning process canbegin, the sensor unit 1 is initialized. One embodiment of thisinitialization process will now be described with reference to FIG. 6.

FIG. 6A is one embodiment of the initialization process 600 for sensorunit 1. Process 600 begins at block 605 with the rotation of mirror 19to a starting position or bearing, which in one embodiment can bedenoted as bearing_((i)), where i=1. As previously mentioned, in oneembodiment stepping motor 22, under the control of microprocessor 35,can be used to rotate the mirror 19. Once the mirror is positioned atthe starting bearing, microprocessor 35 may wait for a predetermineddelay period to allow the mirror 19 to stabilize (block 610). While inone embodiment, this delay may be 1 second, it should equally beappreciated that the delay may be more or less, and may be dependent onthe final system design.

After the mirror has stabilized, at block 615 the microprocessor 35 maythen take a series of signal samples over the course of sample period,which in one embodiment is 1 second. These output samples may then befed through amplifier 41 to the RMS conditioner 37 under the control ofthe microprocessor 35. In one embodiment, the amplifier 41 is alow-frequency amplifier having a passband between approximately 1 and 10Hertz—the frequencies indicative of fire. The amplifier 41 is a lowfrequency amplifier having a passband between approximately 1 and 10Hertz. While the sample rate is a design consideration impacted by manyfactors, including the speed of microprocessor 35, in one embodiment 192samples may be taken during the sample period.

While the microprocessor 35 may fix the sample period to be 1 second asmentioned above, actual detection may only take place after a “settlingin” period. That is, sample period may be divided up into a “settlingin” period and a “detection” period. To that end, in one embodimentevery sample period may contain an approximately 0.3 second segmentduring which the new position is “settled in” in order for the receivedinfrared signal through the sapphire window to the detector to adjust tothe particular level. The requisite RMS analysis may then be performedover the remaining approximately 0.7 seconds before moving to the nextbearing. It should equally be appreciated that numerous other analyticalapproaches (other than RMS) may similarly be used to assign a value tothe received energy.

Process 600 continues to block 620 where the samples are processed bythe microprocessor 35 to compute the number of times the signaltransitions from above the mean value of the sample set to below themean value. This number, referred to as the “zero-crossing” number, is ameasure of whether the signal is “flickering,” as it would in case of afire. A determination may then be made at decision block 630 as towhether a sufficient number of zero-crossings were recorded. If aninsufficient number of zero-crossings are found, then process 600 movesto block 635 where the sample set is discarded and a new set iscomputed. If, on the other hand, there are a sufficient number ofzero-crossings, then process 600 continues to block 640 where an energyvalue may be computed for the bearing in question. In one embodiment,this energy value, or “chip” value, is a measure of the magnitude of thereceived energy. The received energy level can be computed from thesample sets in a number of different ways depending on a myriad offactors, including the complexity of the microprocessor 35. In oneembodiment, the sum of the absolute values of the samples may be used.Alternatively, computing the true RMS value may be used when themicroprocessor 35 is able to provide sufficient computing power.

At this point, a determination is made as to whether the stepping motor22 has caused the mirror 19 to complete a full revolution. If not, thenat block 650, the mirror 19 is incremented to the next bearing fromwhich a new set of samples may then be taken, If, on the other hand, themirror 19 has completed a full revolution, then the initializationprocess 600 continues to FIG. 6B.

Process 600 continues with block 655 of FIG. 6B. After completing arevolution, the collected set of energy values for that revolution maythen be processed to determine the mean and standard deviation values(block 655). If the mean and standard deviation are determined to bestable, process 600 continues to block 670 where a threshold value maythen be computed. If, on the other hand, the mean and standard deviationvales are not stable, then the energy values may be discarded and theinitialization process 600 restarted.

The initialization process 600 culminates with the computation of athreshold value at block 670. In one embodiment, the threshold value iscomputed according to the formula:Threshold=EV_(Mean)+(γ·EV_(SD)),   (1)

where,

EV_(Mean)=the mean of the sampled energy values for a completerevolution;

EV_(SD)=the standard deviation of the sampled energy values for acomplete revolution; and,

-   -   γ=Q⁻¹(Desire False Alarm Rate), where Q⁻¹ is the inverse Q        function.

It should of course be understood that other formulations may be used todetermine the threshold value. For example, in one embodiment themicroprocessor 35 may have an associated memory (not shown) with storedcharacteristics of forest fires, which may serve as the predefinedcriteria of flicker frequency analysis.

Once Process 600 is complete and the threshold value has been computed,the sensor unit 1 may begin to operate in a normal scan mode. Process700 of FIG. 7 illustrates one embodiment of how sensor unit 1 mayoperate in scan mode. In particular, process 700 begins with themicroprocessor 35 rotating the mirror 19 through each bearing andcomputing the received (chip) energy level beginning at bearing_((i)),where i=1. As previously mentioned, the detection of a CO₂ signal at 4.3micrometers is suggestive of a fire. Thus, energy level samples of a 4.3micrometers having “flicker” frequencies of between 1 and 10 hertz canbe effectively used to detect fire.

Each bearing energy value may be compared to a threshold value at block715. In one embodiment, the threshold value is the value calculatedaccording to Formula 1. If the current bearing provides an RMSindication of CO₂ which exceeds the predetermined threshold value,process 700 moves to block 725, where a determination is made as towhether the detected energy value for bearing_((i)) has exceeded thethreshold value a predetermined number of time (N). While in oneembodiment N=2, it should similarly be appreciated that N greater orless than 2. If the threshold value has been exceeded more than N timesfor a given bearing, process 700 will move to block 730 at which pointthe sensor unit 1 may enter a detect mode. In one embodiment, exceedingthe threshold value N times is a possible indication of fire whichrequires additional analysis. The sensor unit's detect mode will bediscussed in detail below with reference to FIG. 8.

If, at block 720, it is determined that the energy value forbearing_((i)) did not exceed the threshold value, then process 700 willcontinue to decision block 735. Similarly, if it is determined at block725 that the energy value for bearing(i) has not exceeded the thresholdvalue N times, then process 700 will also move to block 735.

At decision block 735, a determination is made as to whether the mirror19 has completed one complete revolution. If not, process 700 willincrement the mirror to the next bearing at block 740 and repeat theenergy value detection operation of block 710 for the current bearing.If, on the other hand, a full revolution has been completed, thenprocess 700 moves to block 745 where the previously calculated thresholdvalue may be updated. In one embodiment, energy values for all of thebearings in a revolution may be retained, except for those bearingswhich exceeded the threshold value. At the end of the revolution, themean and standard deviation of those energy values may then be computed(see block 655 of FIG. 6B). In one embodiment, this information may becombined with the previously calculated mean and standard deviationvalues to generate revised EV_(Mean) and EV_(SD) values. In oneembodiment, this combination operation may be performed in an InfiniteImpulse Response (IIR) filter. Regardless of how they are computed, oncethe revised EV_(Mean) and EV_(SD) values have been generated, a revisedthreshold value may then be computed (block 745), which in oneembodiment may be done using Formula 1. The sensor unit 1 may thenrepeat the scan process 700 using this revised threshold value.

FIG. 8 depicts one embodiment of the sensor unit's detect mode. Asmentioned above, in one embodiment the sensor unit 1 may enter detectmode after a given bearing (referred to hereafter as “bearing X”)exceeds the threshold value N times. In the embodiment of FIG. 8, detectprocess 800 begins with the sensor unit 1 taking additional samples atblock 805 for bearing X. To do this, the mirror 19 may remain fixed onthe bearing to be analyzed for a period of time beyond the regularsample period (e.g., 1 second). In one embodiment, the mirror 19 mayremain fixed on the bearing in question for up to three minutes in orderto provide a detailed examination of the radiation entering bearing X.

Once the additional sample data has been collected at block 805, process800 continues to block 810 where the data is normalized. In oneembodiment, this may be done by dividing the total energy received overthe detect period by the number of sample periods in a detect period.For example, in the embodiment where the sample period is 1 second andthe detect period is 5 second, the energy received over the additional5-second detect period would be divided by 5 to scale it back to thesame range as the 1-second samples collected during the scan mode.

Once the additional data has been normalized, the additional samples maythen be compared to the previously-computed threshold value at block815. If it is determined at block 820 that additional sample dataexceeds the threshold level, a fire notification signal may be generated(block 825). In one embodiment, the fire notification signal may includea fire detection signal and a bearing signal, where the bearing signalcan be used by firefighting personnel to determine the location of thefire relative to the sensor unit 1. After the fire notification has beensent, the sensor unit 1 may exit the detect mode and return to the scanmode at block 830. In one embodiment, Scanning continues in scan modewhen a fire is indicated to allow for analysis of the spread of the fireto different bearings and to enable detection of the direction in whichthe fire is spreading. Similarly, if at block 820 the additional sampledata did not exceed the threshold level, then process 800 would skip thenotification operation and move to block 830 where the detect mode maybe exited.

While the preceding description has been directed to particularembodiments, it is understood that those skilled in the art may conceivemodifications and/or variations to the specific embodiments describedherein. It is understood that the description herein is intended to beillustrative only and is not intended to limit the scope of theinvention.

1-29. (canceled)
 30. A method for fire detection comprising: taking aplurality of energy samples during a normal scan mode; computing aplurality of energy values for each of said plurality of energy samples;comparing each of said plurality of energy values to a dynamicallycomputed threshold value based on ambient infrared energy levels;entering a detect mode when one of said plurality of energy valuesexceeds the threshold value more than a predetermined number of timesduring said normal scan mode. generating a fire notification signal ifthe one of said plurality of energy values is greater than saidthreshold value over an extended period of time.
 31. The method of claim30, further comprising filtering said plurality of energy samples to awavelength range centered about 4.3 microns in the infrared spectrum.32. The method of claim 30, further comprising filtering said pluralityof energy samples to a flicker frequency range between 1 and 10 Hertz.33. The method of claim 30, further comprising rotating a mirror of aninfrared sensor in a circular path; pausing said mirror on each of aplurality of bearings along said circular path, wherein each of saidplurality of bearings spans a predetermined number of degrees; andtaking the plurality of energy samples for each of said plurality ofbearings using said infrared sensor during said pausing.
 34. The methodof claim 30, further comprising: taking additional energy samples duringthe detect mode at a bearing corresponding to said one of said pluralityof energy samples; normalizing said additional energy samples; comparingsaid normalized additional energy samples to the threshold value; andgenerating said fire notification signal when said normalized additionalenergy samples exceeds said threshold value.
 35. The method of claim 30,wherein said threshold value is dynamically adjusted based on saidplurality of energy samples.
 36. A system comprising: a sensor forreceiving a plurality of energy samples during a normal scan mode; and aprocessor coupled to the sensor, the processor configured to: compute aplurality of energy values for each of said plurality of energy samples,compare each of said plurality of energy values to a dynamicallycomputed threshold value based on ambient infrared energy levels, entera detect mode when one of said plurality of energy values exceeds thethreshold value more than a predetermined number of times during saidnormal scan mode, and generate a fire notification signal if the one ofsaid plurality of energy values is greater than said threshold valueover an extended period of time.
 37. The system of claim 36, furthercomprising a first filter coupled to the sensor for filtering saidplurality of energy samples to a wavelength range centered about 4.3microns in the infrared spectrum.
 38. The system of claim 37, furthercomprising a second filter coupled to the sensor for filtering saidplurality of energy samples to a flicker frequency range between 1 and10 Hertz.
 39. The system of claim 36, further a mirror controllable bythe processor and configured to direct said plurality of energy samplesto the sensor, said processor being further configured to: rotate themirror of an infrared sensor in a circular path, pause the mirror oneach of a plurality of bearings along said circular path, wherein eachof said plurality of bearings spans a predetermined number of degrees,and take the plurality of energy samples for each of said plurality ofbearings using said infrared sensor during said pausing.
 40. The systemof claim 36, wherein the processor is further configured to: takeadditional energy samples during the detect mode at a bearingcorresponding to said one of said plurality of energy samples, normalizesaid additional energy samples, compare said normalized additionalenergy samples to the said threshold value, and generate said firenotification signal when said normalized additional energy samplesexceeds said threshold value.
 41. The system of claim 37, wherein saidthreshold value is dynamically adjusted based on said plurality ofenergy samples.
 42. A method for fire detection comprising: taking aplurality of energy samples at each of a plurality of bearings along acircular path, wherein each of the plurality of energy samples are takenover a first period of time; computing a plurality of energy values foreach of said plurality of energy samples; comparing each of saidplurality of energy values to a threshold value; determining if thethreshold value has been exceeded at one or more of the plurality ofbearings; taking additional energy samples if the threshold value hasbeen exceeded at one or more of the plurality of bearings, wherein eachof the additional samples are taken over a second period of time, wherethe second period of time is greater than the first period of time; andgenerating a fire notification signal responsive to said additionalenergy samples.
 43. The method of claim 42, further comprising filteringsaid plurality of energy samples to a wavelength range centered about4.3 microns in the infrared spectrum.
 44. The method of claim 42,further comprising filtering said plurality of energy samples to aflicker frequency range between 1 and 10 Hertz.
 45. The method of claim42, further comprising: normalizing said additional energy samples tosaid first period of time; and comparing said normalized additionalenergy samples to the threshold value.
 46. The method of claim 45,wherein said generating comprises generating the fire notificationsignal when said normalized additional energy samples exceed thethreshold value.
 47. The method of claim 42, wherein taking theplurality of energy samples comprises taking the plurality of energysamples during a normal scan mode, and wherein taking the additionalenergy samples comprises taking the additional energy samples during adetect mode.
 48. The method of claim 42, further comprising entering thedetect mode in response to determining that the threshold value has beenexceeded at one or more of the plurality of bearings.
 49. The method ofclaim 42, wherein said threshold value is dynamically adjusted based onsaid plurality of energy samples.